1. Field of the Invention
The present invention relates to an exposure control apparatus for camera, and more particularly relates to an exposure control apparatus having a temperature compensation device for camera.
2. Description of the Prior Art
As is known well, since a photo-electric conversion element for sensing object bright is positioned at a finder optical system, etc. in a single lens reflex camera, incident light into said element is shielded by the mirror up, etc., while shutter is in operation. Therefore, for obtaining appropriate exposure value by controlling an electric shutter circuit from the output of the photo-electric conversion element, it is necessary to memorize the measured value of object brightness before the shutter is activated by some means for example a memory capacitor. Such a memory type electric shutter is publicly known. In such an electric shutter, when object brightness varies over a wide range, memory function with such wide range of level as following said variation is required for a memory capacitor. Furthermore, a timer circuit which is to detect the terminal voltage of said memory capacitor for adjusting the limit time of a shutter must employ a circuit which corresponds linearly to said terminal voltage with wide range. However, since such a circuit and capacitor which satisfies said requirements are expensive and have a complicated circuit arrangement, heretofore a light measuring circuit having a log. diode with logarithmic compression characteristics connected to the above mentioned photo-electric conversion element is employed. Timer action is made based on the compressed photo-electric conversion element output signal, thus eliminating the above mentioned shortcomings of conventional devices.
However, in a device of such type to compress such photo-electric conversion element output, when the timer action is completed, the memorized photo-electric conversion element output is expanded once using an expansion diode, etc. As this expansion diode has large dependence on temperature, accurate shutter speed control cannot be performed constantly in a conventional device.